Temperature Converter — °C, °F, Kelvin & Scientific Scales

How to use this temperature converter

Type a temperature, choose the scale you have, and choose the scale you want. The result appears instantly along with the exact formula used and a table showing your temperature in every scale. Temperatures below absolute zero (−273.15 °C) are flagged as impossible rather than silently converted.

Understanding the temperature scales

Celsius (°C) is the everyday standard in most of the world, defined with water freezing at 0° and boiling at 100° at sea level.

Fahrenheit (°F) is used in the United States. Water freezes at 32 °F and boils at 212 °F. The conversion is °F = °C × 9/5 + 32.

Kelvin (K) is the scientific (SI) scale. It starts at absolute zero — the coldest temperature physically possible — and uses the same step size as Celsius, so K = °C + 273.15. Kelvin has no degree symbol and no negative values.

Rankine (°R) is the absolute version of Fahrenheit, used in some US engineering fields like thermodynamics. Zero Rankine is absolute zero, and one Rankine degree equals one Fahrenheit degree.

Réaumur (°Ré) is a historical scale (water freezes at 0°, boils at 80°) still occasionally seen in old European texts and some traditional cheese and syrup production.

Frequently asked questions

How do I convert Celsius to Fahrenheit in my head?
Double the Celsius value and add 30. It's not exact (the exact formula is ×9/5 + 32), but it gets within a few degrees for everyday temperatures — 20 °C ≈ 70 °F (exact: 68 °F).

What is absolute zero?
−273.15 °C, −459.67 °F, or 0 K — the point at which particles have the minimum possible thermal energy. No temperature can go below it.

At what temperature are Celsius and Fahrenheit equal?
At −40°. It's the single point where both scales read the same number: −40 °C = −40 °F.

Why does science use Kelvin instead of Celsius?
Because Kelvin is an absolute scale starting at zero energy, equations in physics and chemistry (like the gas laws) only work correctly with absolute temperatures.

What is normal body temperature?
Traditionally 37 °C (98.6 °F), though healthy body temperature actually ranges from about 36.1 to 37.2 °C and varies through the day.

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